Ocaml: Getting CPU usage of process

What I want to do

I have a computationally intensive OCaml application and I'd like it to run in the background without disturbing normal computer usage. I'd like to present the users with two options:

(1) the application only runs when CPU usage is virtually 0%;

(2) the application only uses "free" processing power (e.g. if other processes add up to 100%, the OCaml application pauses; if other processes are virtually 0%, then there are no restrictions for the OCaml application; if other processes add up to, say, 50% then OCaml will use up to 50%).

Some thoughts

My idea is to check CPU usage at various check points in the code and pause execution if necessary.

In (1), we just check if CPU is below say 2% and, if not, pause until it becomes lower than 2% again.

In 开发者_StackOverflow中文版(2), things are trickier. Since when no restrictions are present the application always consumes 100% of CPU and checkpoints will be quite frequent, to reduce CPU usage to, say, half, I just have to delay it at every checkpoint by exactly the time it took between check points. If check points are frequent, this would be similar to using 50% CPU, I'd say. For other percentages we can do something similar by suspending for appropriate periods of time. However, this looks very contrived, full of overhead, and above all, I'm not sure it really does what I want. A better alternative could be to invoke Unix.nice n with some appropriate integer at the start of the application. I suppose that setting n=15 would probably be right.

My questions

(Q1) How can I know from within my OCaml application what the CPU usage for the application process is? (I'd like to do this with an OCaml function and not by invoking "ps" or something similar on the command line...)

(Q2) Do you see problems with my idea to achieve (2). Which are the practical differences to changing niceness of process?

(Q3) Do you have any other suggestions for (2)?

Use Caml's Unix library to periodically capture your CPU times and your elapsed times. Your CPU usage is the ratio. Try Unix.gettimeofday and Unix.times. N.B. You'll need to link with the -lunix option.

I too would just run the process under nice and be done with it.

Get your PID then parse the contents of /proc/<PID>/stat to get info about your process and /proc/stat to get global CPU info. They both have a bunch of statistics that you can use to decide when to do work and when to sleep. Do man proc to see the documentation for all the fields (long). Related question with good info: stackoverflow.com/questions/1420426

Setting niceness is easy and reliable. Doing things yourself is much more work but potentially gives you more control. If your actual goal is to just run as a background task, I would go with nice and be done with it.